This non-provisional application claims priority under 35 U.S.C. § 119(a) on Korean Patent Application No. 2004-92468 filed on Nov. 12, 2004, which is herein incorporated by reference.
1. Field of the Invention
Embodiments of the present invention relate to a novel black matrix, a method for preparing the black matrix, and a flat panel display and an electromagnetic interference filter comprising the black matrix. More specifically, embodiments of the present invention relate to a black matrix comprising a substrate, a titanium oxide layer, a Ni plating layer and a Ni/Pd alloy layer; a method for preparing the black matrix; and a flat panel display and an electromagnetic interference filter comprising a black matrix with high blackening density and superior electrical conductivity prepared by the method.
2. Description of the Related Art
Black matrices called “light-blocking films” are currently applied to all display devices to prevent color mixing between red (R), green (G) and blue (B) colors and to improve the image contrast. To prevent deterioration of visibility, black matrices are combined with color filters in liquid crystal displays, are interposed between RGB pixels in luminescent devices, such as fluorescent displays and phosphorescent displays, and are formed by additionally blackening copper wires of electromagnetic interference filters in plasma displays.
Most black matrices developed hitherto are prepared by pattering metal films, e.g., chromium films, by photolithography. In this connection, for example, U.S. Pat. No. 5,378,274 (Yokoyama et al.), U.S. Pat. No. 5,587,818 (S. Lee et al.), and U.S. Pat. No. 5,592,317 (Fujikawa et al.) disclose methods for preparing a black matrix by vacuum-depositing chromium within a display screen to form a light-absorption coating layer and pattering the coating layer by photolithography. These methods, however, entail considerable preparation costs. Further, black matrices prepared by the methods have a high reflectance, and color filters combined with the black matrices have a high light reflectance, causing poor visibility of images.
To solve this problem, there have been proposed various methods for achieving low reflectance characteristics by forming a chromium film between oxide films, such as chromium oxide films. The advantages of black matrices prepared by these methods include high visible light absorption rate, small film thickness, and high optical density. However, the metal chromium may be converted to the chromium (VI) species and the use of heavy metals containing oxidation factors, such as ammonium-cerium (IV), is required, which poses health and environmental hazards.
Thus, there is a strong need in some industrial fields to replace chromium-based materials with organic black matrix coating materials because of the typical advantages of lower price as compared to the chromium-based materials, substantially reduced threat to the environment, and greater ease of pattern formation.
Extensive research and development have been conducted on organic black matrix materials for the past decade. U.S. Pat. No. 4,822,718 (Latharn et al.) and U.S. Pat. No. 5,176,971 (Shimamura et al.) disclose dyed black matrix compositions comprising a polyimide precursor binder. However, these compositions have the problems of short storage life, relatively low optical density after deposition, poor heat stability and fading resistance, and the like. In addition, the “dye-based” compositions tend to dye leachate during subsequent processing steps. Further, since the coating materials do not serve to substantially create photoimages, an additional photoresist layer is necessary to form a pattern.
For achieving higher optical density, improved heat stability and superior fading resistance and resistance to chemical attack, pigment-dispersed (distinguished from “dye-based”) black matrix coating systems have been developed. No pigment-dispersed coating compositions satisfy the requirements on black matrix systems having high electrical resistance, small film thickness and high optical density.
Japanese Patent Laid-open No. Hei 8-34923 (Sekisui Chemical Industries, Ltd.) describes a two-step method for preparing a black matrix by coating a substrate with a composition comprising a photosensitive polymer and a black dye to form a black-colored layer, exposing the layer to light through a mask to form a desired pattern, and colorizing the pattern with a black dye. However, this method is too complicated to be put to practical use.
On the other hand, when organic materials constituting black matrices are frequently exposed to light, display quality is deteriorated and improvement in shelf life is required. Compositions with improved shelf life are described in, e.g., U.S. Pat. No. 5,626,796 (Tsujimura et al.), U.S. Pat. No. 5,639,579 (Hayashi et al.), U.S. Pat. No. 5,714,286 (Uchikawa et al.) and U.S. Pat. No. 5,866,298, and Japanese Patent Laid-open Nos. 2000-147240, Hei 11-143056 and Hei 11-326606. The compositions with improved shelf life described in the patent literature have a problem in that they cannot exhibit high optical density comparable to chromium black matrix systems. The reason is that since resin black matrices have a lower absorption coefficient than metal black matrices, they must have a large film thickness to reach specified optical density. From the large film thickness arises the problem of step height in the subsequent processing, thus deteriorating the driving characteristics of the entire display device.
On the other hand, Japanese Patent Laid-open No. Hei 11-352310 discloses a technique for preparing a black matrix using Ni and NiOx. This technique is environmentally friendly, but requires the use of a different type of vacuum apparatus from conventional vacuum sputtering apparatuses in the formation of a Ni film. In addition, the technique suffers from a difficulty in determining uniform etching conditions.